The present invention is generally related to lithographic duplicators and, more particularly, to a versatile system for controlling ink and moisture feed rates during printing.
The production of quality copies by lithographic means requires that the ink and moisture each be supplied at a rate proper for the demands of the lithographic master. It is also necessary that a proper balance be maintained between the ink and moisture at all times. If the amount of ink or moisture, or the balance therebetween, is not maintained within predetermined ranges, noticeable copy degradation will result. For example, excessive moisture or an excessive moisture/ink ratio will reduce the ink transferred, resulting in copies with low optical density image areas. On the other hand, low moisture or excessive ink will cause the image areas to be blurred and may result in background toning.
In general terms, one of the primary problems over the years has been that the ink and moisture requirements for producing quality copies vary significantly with changes in operating and environmental conditions. For example, variations in temperature and humidity will change the amount of moisture required by the master for quality copies. Also, certain plates or masters, both referred to herein generally as "masters" such as those of the zinc oxide type, undergo changes during copy runs which have an effect upon the amount of moisture required. The moisture/ink requirements also may be affected by the presence of additional moisture introduced into the system as new masters are loaded in sequence for relatively short copy runs, wherein each new master is "wet" and adds moisture to the system.
The present invention addresses the problems presented by the addition of moisture to the duplicator when several relatively short copy runs have been made. In recent years, various duplicators have been proposed or manufactured which include their own master makers and processing equipment, together with means for automaticly loading new masters onto the duplicator's master cylinder. Such processing equipment includes means to render the master background areas hydrophylic. This entails the use of solutions commonly referred to as "starting" solutions which are applied to each master for conversion or etching as the master is fed to the duplicator. When a new master is loaded, a significant residue of the starting solution is introduced to the duplicator. From the standpoint of the ink/moisture balance of the lithographic process, this residue has a similar affect as moisture or wetting solution and therefore influences to some degree the moisture level in the duplicator system.
With some master maker equipped duplicators, the starting solution introduced with new masters has a significant effect upon the moisture level, particularly when several relatively short copy runs are made in sequence. This is compounded by the addition of moisture introduced by the "wetting" cycle for each new master prior to printing. Under these conditions, the moisture added with each new master tends to accumulate in the duplicator system, possibly causing a high moisture condition. With conventional controls, it was necessary for the operator to monitor operation of the duplicator and, when necessary, decrease the moisture feed rate and/or increase the ink feed rate to compensate for such high moisture conditions. For the novice or unskilled operator, such adjustments often proved to be an exercise in frustration. Accordingly, it would be desireable to have a control system which automaticly adjusts the ink and moisture feed rates to compensate for such high moisture conditions commonly associated with multiple short run operations.
Therefore, it is an object of the present invention to provide a novel control system which adjusts the ink and/or moisture feed rates to compensate for additional moisture introduced to the duplicator when making several relatively short copy runs.
Another object of the present invention is to provide a unique control system including circuit means which in effect keeps track of the moisture added with each new master and removed during each copy run in order to compensate for predicted high moisture conditions.
It is a further object of the present invention to provide a versatile ink and moisture control system which is effective to decrease the moisture feed rate and/or increase the ink feed rate in response to copy run length indicative of predicted high moisture conditions.